CN105745562B - The manufacturing method of light polarizing film - Google Patents

Abstract

A method for producing a polarizing film, comprising: carrying out a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less, performing a swelling treatment for taking out after being immersed in a swelling bath, a dyeing treatment for taking out after being immersed in a dyeing bath, immersing in a Crosslinking treatment taken out after the crosslinking bath, method of manufacturing a long polarizing film, reducing both sides of the film taken out of at least one treatment bath selected from the group consisting of a swelling bath, a dyeing bath, and a crosslinking bath The treatment of the amount of liquid adhesion at both ends of the width direction.

Description

Manufacturing method of polarizing film

technical field

The present invention relates to a method for producing a polarizing film usable as a component of a polarizing plate.

Background technique

In conventionally used polarizing films, a dichroic dye such as iodine or a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film. Usually, a protective film is attached to one or both sides of a polarizing film with an adhesive to form a polarizing plate, and it is used in liquid crystal displays such as LCD TVs, personal computer displays, and mobile phones.

Generally, the polarizing film is carried out by immersing a continuously conveyed long polyvinyl alcohol-based resin film in a treatment bath such as a swelling bath, a dyeing bath, and a cross-linking bath in sequence, and performing a series of treatments between these processes. Manufactured by uniaxial stretching.

In recent years, the trend of the market is to increase the size, thickness, weight and cost of raw materials of liquid crystal displays. Therefore, a manufacturing method that can achieve wider and thinner polarizing films has been developed. For example, Japanese Patent Application Laid-Open No. 2004-20633 (Patent Document 1) discloses that when a polarizing film is manufactured from a thinner polyvinyl alcohol-based resin film with a thickness of 65 μm or less, specifically 10 to 50 μm, by applying 1000 N to the film while /m or less tension, while stretching to achieve a thin film production method of polarizing film lightweight.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-20633

Contents of the invention

The problem to be solved by the invention

As mentioned above, although a thinner polarizing film is required, in order to meet this requirement, if a thinner polyvinyl alcohol-based resin film is used as a raw material film, when the film is taken out from the treatment bath, due to the The surface tension of the liquid at both ends in the width direction causes curls that are rounded inward at both ends, or inward folds where the curls are strong and the inwardly curled portion and the inner portion of the film are glued together. The problem. In addition, a film that has been curled or folded inward may also have creases, cracks at the creases, and breakage when it is passed through a press roll or stretched.

Therefore, the object of the present invention is to provide a method for producing a polarizing film from a thinner polyvinyl alcohol-based resin film, which can suppress curling and inward folding at both ends in the width direction of the polyvinyl alcohol-based resin film. .

means of solving problems

This invention provides the manufacturing method of the polarizing film shown below.

[1] A method for producing a polarizing film, comprising performing a swelling treatment of taking out after being immersed in a swelling bath, and a dyeing treatment of taking out after being immersed in a dyeing bath, while conveying a long polyvinyl alcohol-based resin film having a thickness of 65 μm or less. , the cross-linking treatment taken out after immersing in a cross-linking bath, and the method of manufacturing a long polarizing film,

The film taken out from at least one treatment bath selected from the group consisting of a swelling bath, a dyeing bath, and a crosslinking bath is subjected to a treatment for reducing the amount of liquid adhered to both ends in the width direction of the film.

[2] The method for producing a polarizing film according to [1], wherein the treatment of reducing the amount of the liquid adhered includes a treatment of blowing air on the film taken out from the at least one treatment bath.

[3] The method for producing a polarizing film according to [1], wherein the treatment of reducing the amount of the liquid adhered includes a treatment of bringing the thin film taken out from the at least one treatment bath into contact with a roll or a bar.

[4] The method for producing a polarizing film according to [2] or [3], wherein the treatment for reducing the amount of the liquid adhered is performed only on both ends in the width direction.

[5] The method for producing a polarizing film according to [1], wherein the treatment for reducing the amount of the liquid adhered includes directly introducing the film taken out from the at least one treatment bath into a pressing roller arranged horizontally with respect to the ground. deal with.

[6] The method for producing a polarizing film according to [4], wherein the film that has been treated to reduce the amount of liquid adhesion is conveyed using a flat roll.

[7] The method for producing a polarizing film according to [6], wherein the film width just taken out from the at least one treatment bath is equal to or less than the width of the film before being immersed in the treatment bath, and the method is carried out in the treatment bath. Stretch treatment.

[8] The method for producing a polarizing film according to [7], wherein the cumulative stretching ratio of the stretching treatment is 2.0 to 4.5 times.

[9] The method for producing a polarizing film according to [7] or [8], wherein a temperature of a treatment bath for performing the stretching treatment is 15 to 40°C.

[10] The method for producing a polarizing film according to any one of [1] to [9], wherein the at least one treatment bath is a swelling bath and/or a dyeing bath.

[11] The method for producing a polarizing film according to [10], wherein the at least one treatment bath is a swelling bath.

According to the method of the present invention, it is possible to effectively suppress curling and inward folding at both ends in the width direction of the film that have conventionally occurred in a method for producing a polarizing film from a thin polyvinyl alcohol-based resin film.

Description of drawings

[ Fig. 1] Fig. 1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing film according to the present invention and a polarizing film manufacturing apparatus used therefor.

[ Fig. 2 ] A schematic diagram showing an example of treatment for reducing the amount of liquid adhesion using a press roller.

Symbol Description

10 raw material film of polyvinyl alcohol-based resin, 11 feed roll, 13 swelling bath, 15 dyeing bath, 17 crosslinking bath, 19 cleaning bath, 21 drying oven, 23 polarizing film, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41 guide rollers, 50, 51, 52, 53, 54, 55 pressure rollers, 60, 61 blowing device.

Detailed ways

<Manufacturing method of polarizing film>

In the polarizing film of the present invention, a dichroic dye (iodine or a dichroic dye) is adsorbed and aligned on a polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film can generally be obtained by saponification of polyvinyl acetate-based resin. The degree of saponification is generally above about 85 mol%, preferably above about 90 mol%, more preferably above about 99 mol%. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and other copolymerizable monomers other than polyvinyl acetate which is a homopolymer of vinyl acetate. As another copolymerizable monomer, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, etc. are mentioned, for example. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

These polyvinyl alcohol-based resins may also be modified, for example, aldehyde-modified polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. may also be used.

In the present invention, an unstretched polyvinyl alcohol-based resin film (raw material film) having a thickness of 65 μm or less, preferably about 10 to 50 μm, more preferably about 10 to 35 μm, is used as a starting material for polarizing film production. When the thickness of the raw material film is thicker than 65 μm, since the mechanical strength of the film is sufficiently high, curling or inward folding of the end portion in the width direction of the film hardly occurs after the film is taken out of the treatment bath.

The width of the whole roll of film is not particularly limited, for example, it can be about 400-6000mm, but the larger the width of the film, the easier it is to produce curling and inward folding. Therefore, the production method of the present invention is particularly effective when the width of the raw material film is large, specifically, when the film width is 1000 mm or more.

The raw material film is prepared as a long unstretched polyvinyl alcohol-based resin film roll (rolled product).

The polarizing film can be continuously manufactured as a long polarizing film by continuously conveying the above-mentioned raw material film along the film conveying line of the polarizing film manufacturing apparatus and performing a predetermined treatment process. The specified treatment steps include, in order, a swelling treatment step of taking out after immersing in a swelling bath, a dyeing treatment step of taking out the swollen film after being immersed in a dyeing bath, and a cross-linking step of taking out the dyed film after being immersed in a crosslinking bath. joint processing procedure. In addition, between the series of treatment steps (that is, before or during any one or more treatment steps), wet or dry uniaxial stretching treatment is performed. Other processing steps may be added as needed.

Hereinafter, referring to FIG. 1 , the manufacturing method of the polarizing film according to the present invention will be described in more detail. FIG. 1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing film according to the present invention and an example of a polarizing film manufacturing apparatus used therefor. The polarizing film manufacturing apparatus shown in FIG. 1 is to convey the raw material film 10 made of polyvinyl alcohol-based resin along the film conveying path while being continuously unwound from the feed roller 11, and to pass through the swelling bath 13, dyeing film, etc. in sequence. Bath 15, cross-linking bath 17 and cleaning bath 19 are finally formed by drying oven 21. The obtained polarizing film 23 can be directly sent, for example, to the subsequent polarizing plate manufacturing process (step of attaching a protective film to one or both surfaces of the polarizing film 23 ).

In addition, Fig. 1 has shown the example that swelling bath 13, dyeing bath 15, cross-linking bath 17 and cleaning bath 19 respectively establish a groove, but according to needs, any treatment bath (will be as swelling bath 13, dyeing bath) 15. The cross-linking bath 17 and the cleaning bath 19 are generally arranged on the film conveying route, and the tanks containing the treatment liquid for processing the polyvinyl alcohol resin film are collectively referred to as "treatment baths"). More than 2 tanks can also be provided.

The film conveying route of the polarizing film manufacturing apparatus can be configured by disposing guide rollers 30 to 41 that can support the conveyed film at an appropriate position outside the above-mentioned treatment bath, or that can further change the conveying direction of the film, or can press and clamp the conveyed film. The film is configured by pressing rollers 50 to 55 that transmit the driving force due to its rotation to the film, or that can change the conveying direction of the film. For example, guide rollers can be arranged before and after each treatment bath or in the treatment bath, so that the film can be introduced into, immersed in and taken out of the treatment bath [see FIG. 1].

In addition, in the polarizing film manufacturing apparatus shown in FIG. 1 , pressure rolls (press rolls 50 to 54 ) are arranged before and after each treatment bath, and thus, in any one or more treatment baths, pressure rolls arranged before and after it can be used. A difference in rotation speed is set between the press rolls to perform longitudinal uniaxial stretching, and stretching between rolls is performed.

The polyvinyl alcohol-based resin film was taken out of the treatment bath with the treatment liquid adhered to both surfaces. In the present invention, the above-mentioned curling and inward folding should be suppressed, and the polyvinyl alcohol-based resin film taken out from at least one treatment bath selected from the group consisting of the swelling bath 13, the dyeing bath 15, and the crosslinking bath 17 should be reduced. The treatment of the amount of liquid adhered to both ends of the width direction of both sides. Each processing step will be described below.

(swelling treatment)

The swelling treatment is performed for the purpose of removing foreign matter on the surface of the raw material film 10 , removing a plasticizer in the raw material film 10 , imparting easy dyeability, and plasticizing the raw material film 10 . The processing conditions can be determined within a range that achieves the purpose and does not cause defects such as extreme dissolution and devitrification of the raw material film 10 .

With reference to Fig. 1, convey along the film conveying route that guide roller 30～32 and pressing roller 50 construct, raw material film 10 is immersed in swelling bath 13 (the treatment liquid that is contained in the swelling tank) for predetermined time, then take out, by This enables a swelling treatment. The uniaxial stretching treatment may be performed in the swelling bath 13 by utilizing the difference in rotational speed between the press roll 50 and the press roll 51 .

When the raw material film 10 is initially swelled, the temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, and more preferably about 15 to 30°C. The immersion time of the raw material film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In addition, when swelling a film stretched in air in advance, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, preferably about 30 to 60°C. The immersion time of the film is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling bath 13, in addition to pure water, boric acid (Japanese Patent Laid-Open No. 10-153709 ) and chloride (Japanese Patent Laid-Open No. 06-281816 ) can also be used in the range of about 0.01 to 10% by weight. , aqueous solutions of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

In the swelling treatment, the problem that the raw material film 10 swells in the width direction tends to cause wrinkles in the film. As one method for conveying the film while removing the wrinkle, it is possible to use a roll having a spreading function such as a spreader roll, a helical roll, or a mid-high roll on the guide rolls 30, 31, and/or 32, or to use a roll with a spreader function such as a guide roll. Cloth device, bending roll, tenter and other expanding devices. In order to suppress the occurrence of wrinkles, another method is to perform stretching treatment, which is explained in the section of stretching treatment.

During the swelling treatment, since the film also swells and expands in the film conveying direction, when the film is not actively stretched, in order not to cause film slack in the conveying direction, for example, it is preferable to control the pressure rollers 50, 51 disposed before and after the swelling bath 13. speed etc.

In addition, for the purpose of stabilizing the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by spraying in water, or an EPC device (Edge Position Control device: detecting the edge of the film, Devices to prevent the film from traveling in a bend) etc. are also useful.

The film taken out from the swelling bath 13 passes through the guide roller 32 and the press roller 51 in this order, and is introduced into the dyeing bath 15 .

(dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing an alignment dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions can be determined within a range that achieves the purpose and does not cause defects such as extreme dissolution and devitrification of the film. Referring to Fig. 1, it can be transported along the film conveying route constructed by guide rollers 33-35 and pressure roller 51, and the film after the swelling treatment is immersed in the dyeing bath 15 (treatment liquid contained in the dyeing tank) for a prescribed time, and then Take it out, and carry out the dyeing process thereby.

When iodine is used as a dichroic dye, for example, an aqueous solution having a concentration of iodine/potassium iodide/water=about 0.003 to 0.3/about 0.1 to 10/100 in a weight ratio can be used in the dyeing bath 15 . Other iodides such as zinc iodide may be used instead of potassium iodide, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, etc., may coexist. When boric acid is added, iodine is contained, which is different from the cross-linking treatment described later. If the aqueous solution contains more than about 0.003 parts by mass of iodine per 100 parts by mass of water, it can be regarded as the dyeing bath 15 . The temperature of the dyeing bath 15 when immersing the film is usually about 10-45°C, preferably 10-40°C, more preferably 20-35°C, and the immersion time of the film is usually about 30-600 seconds, preferably 60-300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye/water=approximately 0.001 to 0.1/100 in a weight ratio can be used in the dyeing bath 15 . In this dyeing bath 15, dyeing auxiliaries and the like may coexist, and for example, inorganic salts such as sodium sulfate, surfactants, and the like may be contained. The dichroic dye may be used alone or two or more dichroic dyes may be used in combination. The temperature of the dyeing bath 15 when immersing the film is, for example, about 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

In the dyeing treatment step, it is preferable to uniaxially stretch the film in the dyeing bath 15 . The uniaxial stretching of the film can be performed by a method such as a difference in rotational speed between the press roll 51 and the press roll 52 disposed before and after the dyeing bath 15 .

In the dyeing process, in order to transport the polyvinyl alcohol-based resin film while removing film wrinkles similarly to the swelling process, guide rolls 33, 34, and/or 35 can be used with spreading functions such as spreader rolls, spiral rolls, and mid-high rolls. rollers, or fabric guides, bending rollers, tenters and other expanding devices. Another method for suppressing the generation of wrinkles is to perform stretching treatment as in the swelling treatment.

The film taken out from the dyeing bath 15 passes through the guide roll 35 and the press roll 52 in this order, and is introduced into the crosslinking bath 17 .

(cross-linking treatment)

The cross-linking treatment is performed for the purpose of water resistance and color adjustment (prevention of thin bluishness, etc.) through cross-linking. Referring to Fig. 1, it can be transported along the film conveying route constructed by guide rollers 36-38 and pressure roller 52, and the film after the dyeing treatment is immersed in the crosslinking bath 17 (the treatment liquid contained in the crosslinking tank) for a specified time. , and then taken out, thereby performing a cross-linking treatment.

The crosslinking bath 17 may be an aqueous solution containing about 1 to 10 parts by mass of boric acid per 100 parts by mass of water. In the crosslinking bath 17, when the dichroic dye used in the dyeing process is iodine, it is preferable to contain iodide in addition to boric acid, and the amount may be 1 to 30 parts by mass based on 100 parts by mass of water. Potassium iodide, zinc iodide, etc. are mentioned as an iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, and the like may coexist.

In the crosslinking treatment, the concentration of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed according to the purpose. The cross-linking treatment for water resistance and the cross-linking treatment for hue adjustment are not particularly distinguished, and are carried out under the following conditions. The purpose of the cross-linking treatment is to make water resistance by cross-linking. When the polyvinyl alcohol-based resin film is sequentially subjected to swelling treatment, dyeing treatment and cross-linking treatment, the cross-linking bath 17 can be a concentration of boric acid/iodide/water in a weight ratio. =3～10/1～20/100 aqueous solution. If necessary, a crosslinking agent such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and a crosslinking agent may be used in combination. The temperature of the crosslinking bath 17 when immersing the film is usually about 50-70°C, preferably 53-65°C, and the immersion time of the film is usually about 10-600 seconds, preferably 20-300 seconds, more preferably 20-200 seconds. Furthermore, when sequentially performing dyeing treatment and crosslinking treatment on the previously stretched polyvinyl alcohol-based resin film, the temperature of the crosslinking bath 17 is usually about 50-85°C, preferably 55-80°C.

After the crosslinking treatment for water resistance, the crosslinking treatment for hue adjustment may be performed. In the cross-linking treatment for the purpose of hue adjustment, for example, when iodine is used as a dichroic dye, a cross-linking bath with a concentration of boric acid/iodide/water = 1 to 5/3 to 30/100 in a weight ratio can be used 17 . The temperature of the cross-linking bath 17 when immersing the film is usually about 10-45° C., and the immersion time of the film is usually about 1-300 seconds, preferably 2-100 seconds.

The cross-linking treatment may be performed multiple times, usually 2 to 5 times. At this time, the compositions and temperatures of the respective crosslinking baths used may be the same or different as long as they are within the above-mentioned ranges. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for hue adjustment may be performed in a plurality of steps, respectively.

The uniaxial stretching treatment may be performed in the crosslinking bath 17 by utilizing the difference in rotation speed between the press roll 52 and the press roll 53 .

In the cross-linking treatment, in order to transport the polyvinyl alcohol-based resin film while removing film wrinkles similarly to the swelling treatment, guide rolls 36, 37 and/or 38 may be provided with spreader rolls, helical rolls, mid-high rolls, etc. Functional rollers, or fabric guides, bending rollers, tenters and other expanding devices. Another method for suppressing the generation of wrinkles is to perform stretching treatment as in the swelling treatment.

The film taken out from the cross-linking bath 17 passes through the guide roller 38 and the pressure roller 53 in sequence, and is introduced into the cleaning bath 19 .

(cleaning treatment)

The production method of the present invention may include washing treatment after the crosslinking treatment. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film. For example, the cross-linked polyvinyl alcohol-based resin film can be washed by immersing it in the cleaning bath 19 (water), spraying the film with water as a shower, or using them in combination.

FIG. 1 exemplifies a case where a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform cleaning treatment. The temperature of the cleaning bath 19 (water) in the cleaning process is usually about 2 to 40° C., and the immersion time of the film is usually about 2 to 120 seconds.

In addition, in the cleaning process, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, rolls having a widening function such as spreader rolls, spiral rolls, and center-high rolls may be used for the guide rolls 39, 40, and/or 41. , or cloth guides, bending rollers, tenters and other expanding devices. In addition, in the cleaning treatment, stretching treatment may be performed in order to suppress the generation of wrinkles.

(A treatment to reduce the amount of liquid adhered to both ends in the width direction of a polyvinyl alcohol-based resin film)

In the present invention, the above-mentioned curling and inward folding should be suppressed, and the polyvinyl alcohol-based resin film taken out from at least one treatment bath selected from the group consisting of the swelling bath 13, the dyeing bath 15, and the crosslinking bath 17 is subjected to This is a treatment to reduce the amount of liquid adhered to both ends in the width direction of the surface. Both ends in the width direction of the film mean that the sum of both ends is preferably about 2 to 20% of the entire film width. The treatment for reducing the amount of liquid adhesion at both ends in the width direction can be performed, for example, by the following methods 1) to 3).

1) A method of reducing the amount of liquid adhering by blowing air on both sides of the polyvinyl alcohol-based resin film taken out from at least one treatment bath to remove at least the liquid adhering to the surfaces of both ends in the width direction of the film. What Fig. 1 exemplifies is the treatment that uses this method to reduce the amount of liquid adhering. Air blowing devices 60 and 61 are used to spray gas to both ends in the width direction of the film taken out from the swelling bath 13, and to remove the adhering liquid on the surface of the two ends. liquid.

In the example shown in FIG. 1 , when the film taken out from the treatment bath passes through a press roll (press roll 51 in FIG. 1 ), this blowing treatment is performed before passing through the press roll. In addition, in the example shown in FIG. 1, when the film taken out from the treatment bath first passes through the guide roll (the guide roll 32 in FIG. 1 ), and then passes through the press roll (the press roll 51 in FIG. 1 ), the air blowing process also It can be implemented at two places before passing through the guide roller and between the guide roller and the pressure roller (as shown in the example in FIG. 1 ), or only at any one of them. It is preferable that the blowing treatment is performed at least on the film immediately after being taken out from the liquid surface of the treatment bath.

The type of gas used in the blowing treatment is not particularly limited, and is usually an inert gas relative to the thin film, such as air, nitrogen, or argon, preferably air. The injection pressure of the gas is not particularly limited, as long as the attached liquid can be blown away.

In order to suppress curling and inward folding of the film taken out from the treatment bath, it is sufficient to blow air only to both ends of the width direction of the film, but it is also possible to blow air to other film surface areas in addition to the width direction ends. Perform air blowing. For example, air blowing may be performed on the entirety of both surfaces of the film.

The air blowing devices 60 and 61 may be, for example, pipes (pipes) or hoses, air knives, etc. having one or more injection holes for injecting gas.

2) By making both sides of the polyvinyl alcohol-based resin film taken out from at least one treatment bath contact (press) with a roll or a bar, at least the roll or bar is used to remove the liquid adhered to the surface of both ends in the width direction of the film, reducing method of liquid adhesion.

When the film taken out of the treatment bath passes through a press roll (for example, press roll 51 in FIG. 1 ), the contact treatment with the roll or bar is performed before passing through the press roll. In addition, when the film taken out from the treatment bath first passes through a guide roll (eg, guide roll 32 in FIG. 1 ) and then through a press roll (eg, press roll 51 in FIG. 1 ), the contact treatment with this roll or bar can be It may be implemented at two places before the guide roller and between the guide roller and the pressure roller, or may be implemented at only one of them. It is preferably carried out at least before passing through the above-mentioned guide rollers. More preferably, the contact treatment with the roll or bar is performed at least on the film immediately after being taken out from the liquid surface of the treatment bath.

The rolls in contact with the surfaces of both ends in the width direction of the film may be, for example, a pair of rolls that pinch both sides of the polyvinyl alcohol-based resin film taken out from the treatment bath like cloth guides. When the film passes between the pair of rollers, the adhered liquid is peeled off in the surface region in contact with the rollers. On the other hand, the rods in contact with the surfaces of both ends in the width direction of the film do not rotate by themselves like rollers, but sandwich both sides of the polyvinyl alcohol-based resin film taken out from the treatment bath, or contact one side of the film sequentially. A pair of sticks. When using this type of rod, the adhered liquid will also be peeled off in the surface area in contact with the rod through the thin film between the rods.

The surfaces of the above-mentioned rollers and rods that come into contact with the film may be made of metal such as stainless steel, or rubber, sponge or the like. The shape of the roll and the rod may be any as long as the surface in contact with the film is curved, but a cylindrical shape is preferable. When a cylindrical roll or rod is used, its diameter is about 5 to 100 mm, preferably 10 to 50 mm. If the diameter is within this range, the film can be transported smoothly.

In order to suppress the curling and inward folding of the film taken out from the treatment bath, it is sufficient to only make the both ends of the width direction of the film come into contact with a roller or a bar, but it is also possible to remove both ends of the width direction together. This contact treatment is also carried out on other film surface regions. For example, the contact treatment may be performed on the entirety of both surfaces of the film. The installation angle of the rollers and rods is not particularly limited, and the longitudinal direction of the rollers and rods may be parallel to the film width direction, or may be inclined relative to the film width direction.

3) A method in which the polyvinyl alcohol-based resin film taken out from at least one treatment bath is introduced into a press roll, and the liquid adhered to the surface of the film is removed by the press roll to reduce the amount of liquid adhered. In this method, the liquid adhered to the entirety of both surfaces of the film is usually peeled off. An example according to this method is shown in Figure 2.

In FIG. 2 , it is illustrated that the film taken out from the swelling bath 13 is introduced into a press roll. In the example of FIG. 2( a ), first, the conveying direction of the film taken out from the swelling bath 13 is changed by the guide rollers, and then introduced into the press rollers arranged horizontally with respect to the ground. In the example of FIG. 2( b ), the film taken out from the swelling bath 13 is directly introduced into a press roller installed horizontally with respect to the ground. In any example, by arranging the pressure rollers horizontally with respect to the ground, it is possible to prevent the liquid adhering to the film from flowing into both ends in the width direction of the film, so that curling and inward folding at both ends of the film can be more effectively suppressed.

When using the method of 1) or 2) above to treat only the both ends of the width direction of the film to reduce the amount of liquid adhesion, the film taken out from the treatment bath and treated to reduce the amount of liquid adhesion is usually used for the entire width of the cylinder with a constant diameter. Flat roller conveying with shaped guide rollers. That is, when the film taken out from the treatment bath and subjected to the treatment of reducing the amount of liquid adhesion first passes through guide rolls and then passes through press rolls, it is preferable that the one or more guide rolls are flat rolls. By transporting a film that has been treated to reduce the amount of liquid adhesion using a flat roller that is placed horizontally to the ground, it is possible to prevent the liquid at the central portion of the film in the width direction from flowing into both ends during film transport, so that the liquid at both ends of the film can be more effectively suppressed. Curl and fold inwards.

What Fig. 1 exemplifies is that the film taken out from the swelling bath 13 is subjected to the treatment of reducing the amount of liquid adhesion, but this treatment can be performed on at least one treatment bath selected from the group consisting of the swelling bath 13, the dyeing bath 15 and the crosslinking bath 17. Removed from the film. In these treatment baths, curling and inward folding tend to occur due to a large amount of swelling of the film. Therefore, it is preferable to treat at least the film taken out from the swelling bath 13 to reduce the amount of adhering liquid. As an example of a preferred embodiment, there may be mentioned a method in which only the film taken out from the swelling bath 13 is treated to reduce the amount of liquid adhesion, and the film taken out from the swelling bath 13 and the film taken out from the dyeing bath 15 are treated to reduce the amount of liquid adhesion. The way it is handled.

Generally speaking, the higher the temperature of the treatment bath, the easier it is to generate curl and inward folding, but according to the present invention, even if the temperature of the treatment bath is relatively high, the curling and inward folding at both ends of the film can be effectively suppressed. As mentioned above, when the raw material film 10 is initially swollen, the temperature of the swelling bath 13 can be around 10°C to 50°C, but even if the temperature is above 30°C, or even above 35°C, it can effectively suppress the swelling at both ends of the film. curl and fold inward. In addition, as mentioned above, when iodine is used as a dichroic dye, the temperature of the dyeing bath 15 can be about 10 to 45°C, but even if the temperature is above 30°C, or even above 35°C, it can effectively suppress the iodine at both ends of the film. Curl and fold inwards. When a dichroic dye is used as the dichroic dye, even if the temperature of the dyeing bath 15 is high, curling and inward folding can be effectively suppressed in the same manner.

(stretching process)

As described above, between the above-mentioned series of treatment steps (that is, before or during any one or more treatment steps), the raw material film 10 is subjected to a wet or dry uniaxial stretching treatment. A specific method of uniaxial stretching treatment may be, for example, a roll that performs longitudinal uniaxial stretching by setting a rotational speed difference between two press rolls (for example, two press rolls disposed before and after the treatment bath) constituting the film transport path. The inter-roll stretching is, for example, heating roll stretching, tenter stretching, etc. described in Japanese Patent No. 2731813, and the inter-roll stretching is preferable. The uniaxial stretching treatment step may be performed multiple times during the period from the raw material film 10 to the polarizing film 23 obtained.

The final cumulative draw ratio of the polarizing film 23 based on the raw material film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times.

The stretching step can be performed in any treatment step, and when the stretching treatment is performed in two or more treatment steps, the stretching treatment can be performed in any treatment step, but it is preferable to perform the stretching treatment in the swelling treatment step and/or the dyeing treatment step.

As mentioned above, when transporting the film taken out from the treatment bath and subjected to the treatment of reducing the amount of liquid adhesion, in order to prevent the liquid in the central part of the width direction of the film from flowing into both ends during film transport, it is effective to pass through the press roller until the film is transported. guide rollers, use only flat rollers. On the other hand, when the film is immersed in the treatment bath, especially the swelling bath 13 and the dyeing bath 15, the film tends to swell and wrinkle. When only flat rolls are used as guide rolls up to the press roll, in order to suppress such wrinkles, it is preferable to perform stretching treatment in the treatment bath so that the film width immediately after being taken out of the treatment bath is equal to that of the film before immersion in the treatment bath. It is more preferable to carry out the stretching treatment in the swelling bath 13 and/or the dyeing bath 15 (especially the swelling bath 13 ) below the width. This stretching treatment is usually stretching between rolls (longitudinal uniaxial stretching) utilizing a difference in rotational speed between press rolls.

The cumulative stretching ratio in the swelling treatment and the dyeing treatment (the cumulative stretching ratio based on the raw material film 10 ) is preferably 2.0 to 4.5 times, more preferably 2.3 to 4.0 times. If it is within this range, it is easy to achieve stretching treatment in which the width of the film immediately after being taken out of the treatment bath is equal to or less than the width of the film before immersion in the treatment bath.

Film wrinkles caused by swelling are more likely to occur when the temperature of the treatment bath is higher, but through the above-mentioned stretching treatment, even if the temperature of the treatment bath is above 15°C, or even above 20°C, the wrinkles can be effectively suppressed. . In addition, in order not to cause excessive swelling, the temperature of the treatment bath is preferably 40° C. or lower.

(drying treatment)

After the cleaning treatment, it is preferable to perform a treatment of drying the polyvinyl alcohol-based resin film. Drying of the film is not particularly limited, and can be performed using a drying oven 21 . The drying temperature is, for example, about 30-100° C., and the drying time is, for example, about 30-600 seconds.

(other processes)

Processing other than the above-described processing may also be added. Examples of treatments that can be added include, after the crosslinking treatment, immersion treatment in an iodide aqueous solution not containing boric acid (color correction treatment), or immersion treatment in an aqueous solution containing zinc chloride or the like not containing boric acid (zinc deal with).

The thickness of the polarizing film 23 obtained as above is thinner than the raw material film 10, for example, about 5 to 30 μm.

＜Polarizer＞

A polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film produced as above with an adhesive. As the protective film, for example, films made of cellulose acetate-based resins such as triacetyl cellulose or diacetyl cellulose; polyethylene terephthalate, polyethylene naphthalate, and polyethylene terephthalate; Films made of polyester-based resins such as butylene phthalate; films made of polycarbonate-based resins; films made of cycloolefin-based resins; acrylic resin films; polypropylene-based resin films.

In order to improve the adhesion between the adhesive and the polarizing film and/or protective film, corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, and primer coating can be performed on the bonding surface of the polarizing film and/or protective film , saponification treatment and other surface treatments.

The adhesive for laminating the polarizing film and the protective film is not particularly limited as long as the two can be bonded together, but one that satisfies sufficient adhesive force and transparency can be selected. Based on these viewpoints, UV-curable adhesives and water-based adhesives can be used for bonding the polarizing film and the protective film. Examples of the water-based adhesive include, for example, an aqueous solution of a polyvinyl alcohol-based resin or an aqueous solution to which a crosslinking agent has been added, and a polyurethane-based latex adhesive.

The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, a mixture of an epoxy compound and a photocationic polymerization initiator, or the like. In addition, a cationically polymerizable epoxy compound and a radically polymerizable acrylic compound may be used in combination, and as an initiator, a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination.

When an ultraviolet curable adhesive is used, after laminating the polarizing film and the protective film via the adhesive, the adhesive is cured by irradiating ultraviolet rays. The light source of ultraviolet rays is not particularly limited, but preferably has a luminescence distribution below a wavelength of 400nm. Specifically, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal Halogen lamps, etc.

The intensity of light irradiation for curing the ultraviolet curable adhesive is appropriately determined according to the composition of the adhesive, and is not particularly limited, but it is preferable that the intensity of irradiation in the wavelength region effective for activating the polymerization initiator is 0.1 to 6000 mW/ cm ² . By properly selecting the irradiation intensity within this range, the reaction time will not be too long, and the yellowing of the adhesive and the deterioration of the polarizing film caused by the radiant heat of the light source and the heat generated during the curing of the adhesive can be suppressed. The light irradiation time can also be selected according to the adhesive to be cured, and is not particularly limited, but is preferably set so that the cumulative light amount representing the product of the above-mentioned irradiation intensity and irradiation time is 10 to 10000 mJ/cm ² . By appropriately selecting the accumulated light amount within this range, a sufficient amount of active species derived from the polymerization initiator can be generated to reliably advance the curing reaction, and good productivity can be maintained without the irradiation time being too long. The thickness of the cured adhesive layer is usually 0.1 to 10 μm, preferably 0.2 to 4 μm.

When using a water-based adhesive, for example, the adhesive can be evenly coated on the surface of the film or flowed between two films, and the two films are overlapped through the adhesive layer, and the method of laminating and drying by a roller or the like can be used. . It can also be cured at room temperature or slightly higher temperature after drying, for example, at a temperature of about 20-45°C. The thickness of the adhesive layer can be appropriately selected within the range of about 0.001 to 5 μm depending on the type of adhesive and the combination of the two films to be bonded. It is preferably 0.01 μm or more, and more preferably 2 μm or less.

Example

The following examples illustrate the present invention in more detail, but the present invention is not limited by these examples.

<Example 1>

Except using 3 cross-linking baths 17 (hereinafter the 1st cross-linking bath is referred to as 17a, the 2nd cross-linking bath is referred to as 17b, and the 3rd cross-linking bath is referred to as 17c), use the same as shown in Figure 1 Polarizing film manufacturing device The same device manufactures polarizing film. The guide rollers 30-41 all use flat rollers.

First, a polyvinyl alcohol film with a thickness of 30 μm [manufactured by Kuraray Co., Ltd. under the trade name “Kuraray Polyfilm VF-PE #3000”, with a degree of polymerization of 2400 and a degree of saponification of 99.9 mol% or more] was continuously conveyed, and placed in a tank filled with pure water at 20°C. Immerse in the swelling bath 13 for 30 seconds. In this swelling treatment, in order to make the width of the film immediately after taking out of the swelling bath 13 smaller than the width of the film before immersion in the swelling bath 13, a speed difference is set between the press rolls 50 and 51 to perform inter-roll stretching (longitudinal uniaxial stretching). stretch). The draw ratio based on the raw material film 10 was 2.5 times.

For the film taken out from the swelling bath 13, use the air blowing device 60 (air nozzle) arranged before the guide roller 32 and the air blow device 61 (air nozzle) arranged between the guide roller 32 and the pressure roller 51 to blow the air on both sides of the film. Air is sprayed from both ends of the width direction to remove the attached liquid.

Then, the film having passed through the press roll 51 was immersed for 120 seconds in a dyeing bath 15 at 30° C. at a weight ratio of iodine/potassium iodide/water of 0.05/2/100. Also in this dyeing process, in order to make the width of the film immediately after taking out of the dyeing bath 15 smaller than the width of the film before dipping in the dyeing bath 15, a difference in rotation speed is set between the press rolls 51, 52 to perform inter-roll stretching (longitudinal uniaxial stretching). stretch). The cumulative draw ratio in the swelling treatment and the dyeing treatment based on the raw material film 10 was 2.7 times.

Then, in order to implement the first cross-linking treatment for the purpose of water resistance, the film that has passed the press roller 52 is placed in a cross-linking bath 17a at 55°C with a weight ratio of potassium iodide/boric acid/water of 12/4.4/100. Dip for 30 seconds. Also in this first crosslinking treatment, in order to make the film width immediately after taking out from the crosslinking bath 17a smaller than the film width before immersion in the crosslinking bath 17a, the press roller 52 and the crosslinking bath 17a and crosslinking rollers installed in the crosslinking bath 17a Between the baths 17b, a rotational speed difference is set between the press rolls to carry out inter-roll stretching (longitudinal uniaxial stretching). The cumulative draw ratio in the swelling treatment, the dyeing treatment, and the first crosslinking treatment based on the raw material film 10 was 5.5 times.

Then, after immersing the film after the first cross-linking treatment in a cross-linking bath 17b at 59°C having the same composition as that of the cross-linking bath 17a for 30 seconds (second cross-linking treatment), in order to perform cross-linking for the purpose of hue adjustment, For linking treatment, immerse for 15 seconds in a 40° C. crosslinking bath 17 c having a weight ratio of potassium iodide/boric acid/water of 9/2.9/100 (third crosslinking treatment).

Then, the film after the third crosslinking treatment was dipped in a cleaning bath 19 filled with 5° C. pure water, and then passed through a drying oven 21 to dry at 70° C. for 3 minutes to produce a polarizing film 23 .

When the above polarizing film production was carried out continuously for 24 hours, both ends of the film were folded inward in the dyeing bath 15, and when the film passed through the press rollers 52 in this state, creases were formed at the ends of the film, and the film was broken. However, this film was broken only once in 24 hours of operation.

<Example 2>

For the film taken out from the dyeing bath 15, use the air blowing device 60 (air nozzle) that is arranged before the guide roll 35 and the blower device 61 (air nozzle) that is arranged between the guide roll 35 and the pressure roll 52 to blow the air on both sides of the film. Except having blown air to both width direction both ends, and removing the adhering liquid, it carried out similarly to Example 1, and implemented polarizing film manufacture continuously for 24 hours. During the 24-hour operation, no defects such as curling or inward folding at both ends in the width direction of the film and accompanying film creases or breaks were found in any processing steps.

<Example 3>

Polarizing film production was carried out continuously for 24 hours in the same manner as in Example 2, except that a rod was installed before the guide roller 32 instead of an air blowing device, and both ends of the width direction of the film after the swelling treatment were brought into contact with the rod. During the 24-hour operation, no defects such as curling or inward folding at both ends in the width direction of the film and accompanying film creases or breaks were found in any processing steps.

<Example 4>

Production of a polarizing film was continuously implemented for 24 hours in the same manner as in Example 3, except that the rod was brought into contact with the entire width of both surfaces of the film. During the 24-hour operation, no defects such as curling or inward folding at both ends in the width direction of the film and accompanying film creases or breaks were found in any processing steps.

<Example 5>

Except that the temperature of the swelling bath 13 was 30° C. and that the stretching ratio in the swelling bath 13 was 3.0 times based on the raw material film 10 , the production of a polarizing film was continuously implemented for 24 hours in the same manner as in Example 2. During the 24-hour operation, no defects such as curling or inward folding at both ends in the width direction of the film and accompanying film creases or breaks were found in any processing steps.

＜Comparative example 1＞

With respect to the film after the swelling treatment, except that the widthwise both ends of the film were not subjected to the spray air treatment, it was carried out continuously for 24 hours in the same manner as in Example 1 to produce a polarizing film. During the 24-hour operation, both ends of the film were inwardly folded, and the film passed through the pressing roller 51 in this state, resulting in 10 times of film creases or the defect that the creases were cracked.

Claims (10)

1. A method for producing a polarizing film, comprising performing a swelling treatment of taking out after being immersed in a swelling bath, and a dyeing treatment of taking out after being immersed in a dyeing bath while conveying a long polyvinyl alcohol-based resin film with a thickness of 65 μm or less, A method for producing a long polarizing film by taking out a cross-linking treatment after immersing in a cross-linking bath, characterized in that, The film taken out from at least one treatment bath selected from the group consisting of a swelling bath, a dyeing bath, and a crosslinking bath is subjected to a treatment for reducing the amount of liquid adhered to both ends in the width direction. 2. The manufacturing method of the polarizing film according to claim 1, the treatment of reducing the amount of the liquid adhesion comprises the treatment of blowing air on the film taken out from the at least one treatment bath, or the treatment of the film taken out from the at least one treatment bath. A treatment in which a film taken out of a bath is brought into contact with a roll or rod. 3. The method of manufacturing a polarizing film according to claim 2, wherein the treatment for reducing the amount of the liquid adhered is performed only on both ends in the width direction. 4. The method of manufacturing a polarizing film according to claim 1, wherein the process of reducing the amount of the liquid adhered includes directly introducing the film taken out from the at least one treatment bath to a press roller arranged horizontally relative to the ground. deal with. 5. The method of manufacturing a polarizing film according to claim 3, wherein the film subjected to the treatment for reducing the amount of adhesion of the liquid is conveyed using a flat roll. 6. The manufacturing method of a polarizing film according to claim 5 , in order to make the film width just after being taken out from the at least one treatment bath be less than the film width before being immersed in the treatment bath, pulling is carried out in the treatment bath. stretch processing. 7 . The method for producing a polarizing film according to claim 6 , wherein the cumulative stretching ratio of the stretching treatment is 2.0 to 4.5 times. 8 . The method for producing a polarizing film according to claim 6 , wherein a temperature of a treatment bath for performing the stretching treatment is 15 to 40° C. 8 . 9. The method for producing a polarizing film according to any one of claims 1 to 8, wherein the at least one treatment bath is a swelling bath and/or a dyeing bath. 10. The method for producing a polarizing film according to claim 9, wherein the at least one treatment bath is a swelling bath.